The patent relates to a delivery system in which a catheter carries a stent on its distal end portion. The stent may be held in place around the catheter prior to and during percutaneous delivery by means of one and preferably two end sleeves, or the stent may be crimped to hold it in place. The stent may be self-expanding, such as a NITINOL shape memory stent, or it may be expandable by means of an inflatable portion of the catheter, such as a balloon. The inflatable portion or balloon is configured to have rounded ends, with the end sleeves overlying the ends of the balloon and shaped correspondingly.
Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Both self-expanding and inflation expandable stents are well known and widely available in a variety of designs and configurations. Self-expanding stents must be maintained under positive external pressure in order to maintain their reduced diameter configuration during delivery of the stent to its deployment site. Inflation expandable stents are crimped to their reduced diameter about the delivery catheter, then maneuvered to the deployment site and expanded to the vessel diameter by fluid inflation of a balloon positioned between the stent and the delivery catheter. The present invention is particularly concerned with delivery and deployment of inflation expandable stents, although it is generally applicable to self-expanding stents when used with balloon catheters.
An example is the stent described in PCT Application NO. 960 3092 A1, published Feb. 8, 1996, the content of which is incorporated herein by reference.
In advancing an inflation expandable stent through a body vessel to the deployment site, there are a number of important considerations. The stent must be able to securely maintain its axial position on the delivery catheter without translocating proximally or distally and especially without becoming separated from the catheter. The stent, particularly its distal and proximal ends, must be protected to prevent distortion of the stent and to prevent abrasion and/or reduce trauma of the vessel walls.
Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al., relates to an inflation expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. During inflation of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar, relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al., describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site. The content of all of these patents is incorporated herein by reference.
In previous inflatable stent delivery systems which utilize an inflatable portion (balloon, etc) to deliver the stent, the balloon is constructed and arranged to include a stent mounting region located between two end cones. The design of such a balloon usually has end cones oriented in a standard uniform 45 degree angular cone extending from the catheter shaft to the stent mounting region of the balloon. A prior stent delivery catheter having a balloon with cone shaped ends is shown in FIG. 4.
The end cone shape described above, provides the ends of a stent delivery balloon with expansion characteristics which are well known to those of ordinary skill in the art and described in greater detail below. However, a balloon having such cone shaped ends may not be ideal for use with a stent delivery system which utilizes socks, sheathes or sleeves as shown in FIG. 1 to retain the stent on the balloon.
When such a balloon with cone shaped ends is utilized in a stent delivery system having retaining socks, sheathes, or sleeves, as described above, the sleeves may not uniformly release the stent or the stent may fail to release at all when the balloon is inflated under low pressure, such as a pressure value between approximately 4 to 10 ATM. The failure to release the stent is due to an insufficient increase in length of the cone shaped ends when the balloon is inflated under low pressure. While it may be possible to use higher pressure, such as a pressure value between approximately 10 to 18 ATM to further expand the balloon ends, this may be undesirable as such increased pressure may cause the balloon and/or vessel to distort or rupture.
The present invention overcomes these problems by providing an inflatable portion, balloon or other type of expandable device, which has rounded ends as opposed to the more common cone shaped ends described above. Relative to the 45 degree angle oriented cone shaped ends of previous balloons, the rounded ends of the present balloon provide additional length to the balloon when it is inflated. As a result the present stent delivery system has improved capability to more effectively remove the sleeves, socks, etc from the stent.
In order to safely and effectively advance a stent delivery catheter through the tortious and narrow confines of various bodily vessels, it is well known that it is desirable to have a stent delivery system with a reduced profile prior to delivery of the stent. However, in order to remove the catheter from the body and minimize damage to any bodily vessels through which the catheter may be drawn, it is also desirable to provide a stent delivery system with a reduced profile subsequent to stent delivery.
To provide the balloon with a reduced profile subsequent to stent delivery, most prior stent delivery systems rely on deflation of the balloon, by simply drawing inflation fluid from the catheter. This method is insufficient, as the balloon may remain in a somewhat enlarged and/or distorted state even after removal of all inflation fluid. As a result of this shortcoming, it would be advantageous to provide a stent delivery system which has a balloon that could be collapsed more effectively. This would provide the catheter with the desirable post stent delivery low profile, allowing the catheter to be safely and readily withdrawal from a bodily vessel and the deployed stent and into the guiding catheter. The present invention provides such a stent delivery system and is described below.
The present invention provides a stent delivery system having an inflatable portion or balloon which has rounded ends rather than the more common conical shaped ends. Balloon ends which are rounded provide increased end length when the balloon is inflated. Depending on the precise shape of other rounded balloon ends varying end length increases will be provided for. Preferably, the present balloon ends are hemispherical.
The hemispherical ends of the balloon provide at least an 11 percent increase in end length when the balloon is inflated under low pressure between approximately 4 to 10 ATM. This increase in end length is in comparison to a similar balloon of like material, inflated under the same pressure, but having coned shape or conical ends, where the conical ends are uniformly disposed about the longitudinal axis of the catheter at an angle of approximately 45 degrees. The increased length of the rounded balloon ends in the inflated state, provides the present invention with superior ability to retract the retaining sleeves from the stent margins when the balloon is inflated to low pressure.
The present invention includes retaining sleeves which overlie the rounded ends of the balloon. Subsequent to stent delivery and deflation of the balloon, the rounded balloon ends and the correspondingly shaped retaining sleeves cooperatively function to compress the balloon ends. This feature provides the balloon with a more collapsed configuration than the balloon would otherwise have relying on deflation alone, and provides the delivery catheter with the desired low profile for withdrawal as described above.
In addition, the unique configuration of the balloon ends and retaining sleeves of the present invention, provides an improvement over the prior art by providing a stent delivery system which requires no lubrication between the balloon or stent surfaces, and the inside surfaces of the retaining sleeves.